In cases of medical intervention in which an instrument has to be inserted into a body cavity, it is often expedient to guide the instrument by means of a flexible shaft, since in many cases treatment is very difficult otherwise, and the use of flexible instruments causes the patient less pain than the use of rigid instruments. Thus, it is often necessary during endoscopic diagnosis and therapy, for example, to be able to bend at least the distal end of the instruments used in different directions inside the body cavity, and in addition, to be able to leave the shaft in this bent position.
For example, according to DE-AS 1 019 048, it is known that a thin-walled instrument shaft can be bent into the desired shape before use and can then, for example, be guided into a body cavity. However, a disadvantage of an instrument of that type is that it can only be inserted in a limited way, since the position that is set once before the treatment cannot be further altered.
Beyond that, bendable arrangements of tubes and shafts for use in an endoscope, especially for example in the area of bronchoscopy, are known in which the arrangement of tubes has, at least in part, regions of segments that are arranged together in a series and that are movable against each other, whereby for the purpose of setting shaft curvatures, the segments can be moved by means of control wires that are guided into a handle. Examples of these are set forth in DE-GM 69 38 905, U.S. Pat. No. 3,190,286, DE-AS 1 291 437, DE-OS 1 766 209, DE-AS 1 816 973, and DE-OS 1 950 035. In the case of DE-AS 1 816 973, the individual segments of the shaft are linked with one another by means of forks that interlock when the components are joined together. A solution of that type proves to be disadvantageous, since the forks of the segments can easily break or become deformed.
These solutions can be used with varying degrees of success for endoscopy, but they all have the disadvantage that when they are in the distorted state, that is when the curvature of the distal end of the shaft has been established and manipulation of instruments is to be undertaken in the body cavity, no real rigidity of the shaft can be attained, and, due to the unavoidable effects of forces on the shaft from the instrument that has been guided into position, the shaft can easily deviate from the desired position.
With these shafts the characteristics of a rigid shaft cannot be attained, while pre-curved shafts, such as those known from DE-AS 1 019 048, can be used only in a limited manner since they retain during use the shape that was set ahead of time. For that reason, the solution in accordance with DE-OS 1 766 209, in which the groups composed of individual segments can be moved independently of each other by means of wires, is better overall. However, the position that is set cannot be fixed with this solution.